a. Field of the Invention
The invention relates to sub-surface soil moisture sensors for use with irrigation systems. More particularly, the invention relates to sensors which employ the use of a float assembly and electronic means to cancel the activation of an automatic sprinkling system when sufficient moisture is in the soil, thus conserving water and preventing over-watering.
b. Description of the Prior Art
Moisture sensors have been disclosed in prior art, including those which measure moisture in the air and provide a means of transmitting a reading to a remote location, and those which measure ground moisture or soil moisture and provide a means of transmitting the reading to a remote location. Of the ground or soil moisture sensors, there are principally two types in prior artxe2x80x94those which use a pneumatic or pressure means and those which employ a dielectric, electro-voltaic or electrical conductivity/resistivity measurement means. Additionally, there are those type moisture measuring devices which are placed above the ground and have a xe2x80x9crain-catchingxe2x80x9d pan with a float-type measuring device which captures and contains rain in the pan elevating a float activating a mechanical switch, similar to a toilet tank float mechanism.
U.S. Pat. No. 5,749,521, to Lattery, discloses an apparatus for soil irrigation control comprising a control unit, a soil probe, and a temperature probe. A relative measurement of soil moisture is accomplished by measuring the voltage potential difference that occurs between the two electrodes of the soil probe while a pulse of electric current passes from one electrode to the other through the surrounding soil. Lattery also incorporates a temperature probe to help compensate for the fact that the apparent resistance of an electrolyte, which the soil medium is assumed to be for these type of devices, decreased with increasing temperature in a very significant manner, due primarily to increasing ion mobility with increasing temperature. Specifically, it is typically estimated that, regardless of ion type, a two percent per degree Celsius change in resistivity is experienced. In order for systems such as Lattery to operate properly, the soil sensor must be in intimate contact with the soil. This present a problem in soil systems where there is a significant clay component. Clay expands and contracts in response to temperature and moisture content variations. Thus, as clay soils dry and contract, they may loose contact with the sensor. Thus, the resistance to the circuit would be increased. The contact may not be re-established when the soil is wetted. Therefore, although the clay soil may be damp, the resistivity would still apparently be high, calling for moisture even when it was not needed. In addition, as noted by Bancroft in U.S. Pat. No. 5,148,985, col. 1, line 51, such sensors tend to rather quickly degrade or corrode. This degrading or corroding causes increased sensor resistance which renders the sensor virtually useless.
Hunter, U.S. Pat. No. 3,981,446, discloses a water operated control apparatus and method based on the principle that air will bubble through dry soil easier than it will bubble through wet soil. It is known that certain materials, such as soil, may allow air to pass therethrough when dry, but prevent the passage of air therethrough when saturated with water. Devices incorporating such moisture sensitive air valves are known in the art. They comprise porous ceramic or plastic materials which have the ability to pass air or not, depending on the amount of their water saturation. The device disclosed by Hunter utilizes this principle to control whether a sprinkler system is turned on or not. The air valve is disposed in the ground, and, in contact therewith, absorbs water from the soil. If the soil is sufficiently saturated, air will not pass through the air valve theoretically. The problem with devices such as that disclosed by Hunter are that where the water is not soft water, i.e., contains a large amount of dissolved minerals and the like, they tend to become clogged. Once they become clogged, they do not operate at all.
Therefore, there is a need for in-ground soil moisture sensor, which overcomes the various disadvantages of the prior art.
The invention is an in-ground sensor having an exterior porous filter, a porous inner screen finer than the outer filter designed to further filter solid particles from the inner portion of the device, a float assembly with a sliding member moving upward in response to buoyant forces, and an electronic means for communication with a control device which sends a signal indicating the level of moisture within the device proportional to the level of the float. The components of the invention are preferably made of a material which is temperature and corrosion-resistant in an environment which may be constantly or repeatedly exposed to moisture and dramatic temperature variation.
The present invention is buried underground. As moisture in the soil increases, it migrates through the exterior filters into a cylindrical void space defined by a inner screen filter. The amount of water standing in the void space lifts a float via buoyancy. Once the float is lifted to a preset level, it can be inferred that soil moisture is adequate, and a contact is disengaged preventing the sprinklers from operating.
There have thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in this application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Additional benefits and advantages of the present invention will become apparent in those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
Further, the purpose of the foregoing abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially the scientist, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is neither intended to define the invention of the application which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way.